Field of the Invention
The present invention relates to a lens apparatus and more particularly to a lens apparatus for broadcast and/or cinema use. The present invention also relates to an image pickup apparatus having such a lens apparatus.
Description of the Related Art
In the broadcast and cinema industries, use of processing such as CG compositing and augmented reality (AR) in the virtual studio has been increasing, and the image resolution is shifting from the high vision to 4K and 8K. Moreover, increasing screen sizes require improvements in accuracy of compositing and increases in the processing speed. Some lens apparatuses are adapted to output relative zoom position information as position information of the lens for virtual processing. However, the zoom position information depends on the optical and mechanical design of the lens apparatus and does not take account of the field-of-view change rate. With improvement in the performance and reduction in size and weight, lenses of which the change of the field-of-view change rate with zooming is not simple have been developed.
The relationship between the virtual values output from lenses used for CG compositing or the like and the optical characteristics of the lenses has variations specific to the lenses that result from manufacturing errors of the lenses and flange-back adjustment.
In view of this, in the case where processing such as CG compositing and/or AR processing is to be used, relationship between virtual output information corresponding to the lens position at which compositing is to be performed and the size of an object in the image is measured in advance. In cases where zoom lens position information is displayed in the viewfinder of the camera, the relative position information of the zoom lens is obtained from the lens apparatus and the value thus obtained is displayed. Japanese Patent Application Laid-Open No. H11-211962 discloses a technology of changing the relationship between the focal length and the field-of-view change rate of a zoom lens. Japanese Patent Application Laid-Open No. 2013-175924 discloses a technology of controlling the drive speed taking account of the field-of-view change rate associated with a zoom position command value when presetting the zoom and pan/tilt.
However, systems that perform processing such as CG compositing and/or AR processing using relative zoom position information as a virtual output value suffers from the following problem. If zoom is controlled based on a command with a constant change speed of zoom lens position, the position of the zoom lens is not changed at a constant speed (or at a constant field-of-view change rate) actually, so that the virtual output value is not output at a constant change rate. Another problem that arises in the case where processing such as CG compositing and/or AR processing is to be performed is that preparation for image taking require time, because measurement of relationship between virtual output information corresponding to the lens position at which compositing is to be performed and the size of an object in the image is performed in advance.
Moreover there is another problem that relative zoom lens position information displayed in the viewfinder of the camera is not displayed at a constant change rate, though the zoom lens is driven by a command with a constant zoom speed. Consequently, in the case of a camera apparatus in which relative zoom lens position information is displayed, the change rate of the relative zoom lens position information is not constant. Therefore, even if the operator intends to shift the zoom position at a constant speed, the displayed position information does not change at a constant change rate. Then, there is a possibility that the operator may mistakenly think that he or she is operating the zoom lens in a wrong way.